This invention relates to an O-ring seal for retaining the lubricant around the journal bearings in a rock bit or drill bit for drilling oil wells or the like. More particularly, this invention relates to an O-ring seal comprising a polarized graphite lubricant additive that reduces friction, improves wear resistance, reduces abrasion, and reduces stick-slip between the O-ring seal and interfacing rock bit surfaces to enhance the service life of the O-ring seal and rock bit.
Heavy-duty drill bits or rock bits are employed for drilling wells in subterranean formations for oil, gas, geothermal steam, minerals and the like. Such drill bits have a body connected to a drill string and a plurality, typically three, of hollow cutter cones mounted on the body for drilling rock formations. The cutter cones are mounted on steel journals or pins integral with the bit body at its lower end. In use, the drill string and bit body are rotated in the bore hole, and each cone is caused to rotate on its respective journal as the cone contacts the bottom of the bore hole being drilled. As such a rock bit is used for drilling in hard, tough formations, high pressures and temperatures are encountered.
When a drill bit wears out or fails as a bore hole is being drilled, it is necessary to withdraw the drill string for replacing the bit. The amount of time required to make a round trip for replacing a bit is essentially lost from drilling operations. This time can become a significant portion of the total time for completing a well, particularly as the well depths become great. It is therefore quite desirable to maximize the service life of a drill bit in a rock formation. Prolonging the time of drilling minimizes the time lost in xe2x80x9cround trippingxe2x80x9d the drill string for replacing the bits. Replacement of a drill bit can be required for a number of reasons, including wearing out or breakage of the structure contacting the rock formation.
One of the consistent problems in drill bits is the inconsistency of service life. Sometimes bits are known to last for long periods, whereas bits which are apparently identical operated under similar conditions may fail within a short lifetime. One cause of erratic service life is failure of the bearings. Bearing failure can often be traced to failure of the seal that retains lubricant in the bearing. Lubricant may be lost if the seal fails, or abrasive particles of rock may work their way into the bearing surfaces, causing excessive wear.
Rock bit elastomeric O-rings and the like are being called on to perform service in environments which are extremely harsh. Modern bits are being run at exceptionally high surface speeds, sometimes more than 500 feet per minute, with cone speeds averaging in the range of from 200 to 400 revolutions per minute. One face of the O-ring or the like is exposed to abrasive drilling fluid and mud. The life of the O-ring may be significantly degraded by high temperatures due to friction (as well as elevated temperature in the well bore) and abrasion.
In order to provide a consistently reliable seal for maintaining the lubricant within rock bits, it is known to make the O-ring seal from a resilient elastomeric composition displaying a desire degree of chemical resistance, heat resistance, and wear resistance. O-ring seals known in the art are constructed from resilient elastomeric materials that, while displaying some degree of chemical, heat, and wear resistance, ultimately limit the service life of the rock bit by wearing away along the surface during use.
Attempts have been made to improve O-ring properties of wear resistance by adding lubricant additives to the elastomeric composition. U.S. Pat. No. 5,402,858, for example, discloses an O-ring seal formed from an elastomeric material comprising low-friction wear resistant particles distributed therein. The wear resistant particles were selected from the group including copper, bronze, brass, nickel, cobalt, cemented tungsten carbide, and titanium carbide. It has been discovered that while such exemplary O-ring seal constructions displayed reduced properties of stick-slip, they were not completely effective at reducing friction and abrasion between the interfacing O-ring seal and rock bit surface.
It is therefore desirable to provide a consistently reliable O-ring seal for maintaining the lubricant within a rock bit, that has a long useful life, is resistant to crude gasoline and other chemical compositions found within oil wells, has high heat resistance, is highly resistant to abrasion, has a low coefficient of friction against the adjacent seal surfaces to minimize heating and wear, and that will not readily deform under load and allow leakage of the grease from within the bit or drilling mud and debris into the bit.
There is, therefore, provided in practice of this invention an improved O-ring seal for rock bit bearings comprising a body formed from an elastomeric material and including a lubricant additive. The lubricant additive is formed from polarized graphite.
O-ring seals made from elastomeric compositions of this invention comprise in the range of from about 50 to 99 percent by volume elastomeric material, and in the range of from about 1 to 50 percent by volume of polarized graphite based on the total volume of the composition. Wax may also be included in the composition.